The next morning, full of new calories from the crawfish-and-clam dinner we'd scavenged from the riverbed, we all slept in. Before he'd left, Cody had given us instructions: Wait until noon, then cut down two willow trees each and head upstream until we saw him. We found him half a mile upriver, waiting in a clearing.

As we sat, he gave a short talk about what we'd done so far. "Every one of your ancestors lived like this," he told us. "I wanted you to tap into that lineage." Robin pointed out that the Drifter mirrored the march of civilization: We'd started out wandering the desert, harnessed fire and built tools, and eventually found a nice place to settle with clean water and access to food. Cody nodded. "It also mirrors resources," he said. "The first night was about thermoregulation. Then water. Then eventually food. It's a hierarchy of need." Cody said that in the college classes he teaches, sometimes kids show up to get away from modern life. "They want to 'get back to the land,' " he said. "They want to make moccasins. They want to make a drum and dance." He shook his head pityingly. "You dance when the pot is empty. Or when it's just been filled."

Everyone said they'd be taking different things away from their experience on the Drifter. Susan, the healer from Peru, said she learned she had more perseverance than she thought – that she could push on for miles with rocks in her shoes, instead of stopping every five minutes to readjust her backpack. Zach, the programmer, said he realized how easy it is to be nice when you're comfortable: "But when you're hot, hungry, have a headache, and can still smile and be pleasant . . . wow. Amazing." And I felt humbled and grateful for people who had skills and knowledge that I didn't – particularly the ones I'd underestimated.

On the dinner menu: riverbed-scavenged crawfish.

My favorite reaction came from Sam, the ex-Navy mechanic. For much of the trip, he had quietly steered us toward the right thing to do without seeming like he was telling us what to do at all. That morning he opened up. Sam said he'd grown up camping and canoeing in Maine, but he was usually alone. "I was closed off," he said. "But what I've learned from being with you all week is, I should have been doing it this way all along. You're supposed to take friends. You're supposed to share it."

Cody said he devised the Drifter to punish us physically, but that most of the benefits were psychological. "It's designed to teach people the difference between what they want and what they need," he told me. "It's designed to teach people to be grateful for what they have. It's designed to remind people of what their ancestors did on a daily basis. But really," he said, "it's about shattering limitations. When someone successfully completes the Drifter, it's a huge confidence booster. If you're ever in a life-threatening situation, your adrenaline starts pumping – but now you know it's going to be OK. You've done this before. You've been in the backcountry for multiple days with limited gear, and you came out OK. How many other Americans can say that?"

Then Cody stood up and clapped his hands. "OK. So what's on the menu right now – and I mean that very much not literally" – he laughed – "is we're going to make a sweat." Sweat lodges, he explained, have been used by indigenous peoples for centuries, for reasons both physical and spiritual. Cody showed us how to bend the willow trunks in the shape of a dome, and how to lash the ends together with strips of bark. We dug a pit to fill with hot rocks, and then covered the whole thing with a tarp. Once night fell, we all crawled inside. Cody the shaman poured cold water on the rocks, and the dome filled with steam.

"A lot of people, whether they know it or not, come on the Drifter for purification," he said. "The desert is like a self-cleaning oven. It bakes the bullshit away. Everything's out there for you to see." Just when the heat got too much to bear, he led us out to the river, and we all plunged in. The water was so cold, we had trouble breathing, but as our bodies adjusted, we started to laugh – first out of relief, then pleasure, then joy. We lay in the mud for a while, our heads steaming, gazing at the stars. Above us, the handle of the Big Dipper pointed the way home.